The present invention relates to a compact imaging optical system and ocular optical system which have favorable aberration correction performance, a wide field angle and high resolution. The present invention also relates to an image display apparatus which uses the ocular optical system.
In recent years, helmet- and goggle-type head- or face-mounted image display apparatuses have been developed for virtual reality or for the purpose of enabling the user to enjoy a wide-screen image personally.
For example, Japanese Patent Application Laid-Open (KOKAI) No. 2-297516 discloses an image display apparatus including, as shown in FIG. 48, a two-dimensional display device 21 for displaying an image, an objective collimator lens 22, and a parallel transparent plate 23 having off-axis parabolic mirrors at both ends thereof. Display light emanating from the two-dimensional display device 21 is formed into parallel rays through the objective collimator lens 22. Thereafter, the light rays are successively subjected to first transmission by one of the parallel surfaces of the parallel transparent plate 23, reflection by the first parabolic mirror, some total reflections in the parallel transparent plate 23, reflection by the second parabolic mirror and second transmission by the other of the parallel surfaces (a total of 8 reflections and a total of 2 transmissions), thereby forming an intermediate image at the point F and projecting the intermediate image into an observer's eyeball 24.
U.S. Pat. No. 4,026,641 discloses an image display apparatus in which, as shown in FIG. 49, an object image displayed by an image display device 25 is converted into a curved object image by a transfer optical element 26, and the object image is projected into an observer's eyeball by a toric reflecting surface 27.
In head-mounted image display apparatuses, it is important to lead an image of an image display device to an observer's eyeball without using a relay optical system and without forming an intermediate image in the optical path, as shown for example in Japanese Patent Application Laid-Open (KOKAI) No. 6-308424.
However, in Japanese Patent Application Laid-Open (KOKAI) No. 6-308424, the optical path is formed with a half-mirror interposed therein. Therefore, there is a loss of light quantity, and it is not easy to perform bright display.
European Patent No. 0,583,116A2 discloses a head-mounted image display apparatus which is capable of displaying a bright image without using a half-mirror. In this case, however, a relay optical system is used, which causes the size of the apparatus to increase unfavorably.
In an image display apparatus of the type in which an image of an image display device is relayed, as shown in FIG. 48, a relay optical system is needed in addition to an ocular optical system. Consequently, the entire optical system increases in both size and weight, and an amount by which the optical system projects from the observer's face or head also increases. Therefore, this type of image display apparatus is not suitable for use as a head- or face-mounted image display apparatus.
In the optical system that focuses parallel rays to form an intermediate image, and also in the optical system that projects an intermediate image into an observer's eyeball, only the parabolic mirror has power. Therefore, exceedingly large aberrations are produced in these optical systems.
When a concave mirror alone is used as an ocular optical system as shown in FIG. 49, even if the concave mirror is a toric surface as in the case of FIG. 49, the ocular optical system produces exceedingly large aberrations, causing the image quality to be degraded. Accordingly, it is necessary to use a transfer optical element 26 such as a fiber plate for correcting field curvature produced by the ocular optical system. However, comatic and other aberrations cannot satisfactorily be corrected even if the transfer optical element 26 and the toric reflecting surface 27 are used.